-LRB- CNN -RRB- -- The man police say opened fire inside a crowded Colorado movie theater may have been planning the attack for months , the local police chief told reporters Saturday .

Suspect James E. Holmes , 24 , is accused of killing 12 people and wounding 58 in the suburban Denver community of Aurora . He is also alleged to have rigged his apartment with booby traps so that whoever entered it would be seriously hurt or killed .

Holmes received a high volume of deliveries over the past four months to both his home and work addresses , which police believe begins to explain how he got his hands on some of the materials used in the attack and those found at his apartment , said Aurora Police Chief Daniel Oates .

`` What we 're seeing here is evidence of , I think , some calculation and deliberation , '' he said . `` We have the evidence of a deliberative process to commit this assault , and we have the evidence of a deliberative process in his mind to attack whoever opened the door of his apartment . ''

`` Make no mistake , '' said Oates , `` this apartment was designed ... to kill . ''

Authorities continued Saturday making headway on the suspect 's home .

Technicians , with the help of a robot , worked to handle traps , wires and possible explosive and incendiary devices , according to Jim Yacone , a special agent with the FBI who briefed reporters alongside Oates . Two devices were intentionally detonated at the site .

The operation proceeded with an eye toward preserving evidence , all of which will be sent to an FBI lab in Quantico , Virginia , Yacone said .

By Saturday evening , police said that `` all hazards '' had been removed from the suspect 's apartment .

Hundreds of residents were evacuated from five buildings , including the modest , three-story brick building where Holmes told police he had rigged his top-floor , one-bedroom apartment with explosives . All occupants except those who live in the suspect 's building were allowed to return home Saturday night , police said .

Remembering the victims through photos

At least 26 victims of the shooting remained hospitalized Saturday -- nine in critical condition -- in five hospitals .

Grief counselors were staffing area high schools . And the city is planning a vigil Sunday night .

Also Sunday , President Barack Obama is expected to be in Aurora to meet with local officials and victims ' families .

`` I think that overall the community is very , very shaken , and I think we 're in shock and I think we 're still trying to get our arms around how did such a tragedy happen to us , '' said Rhonda Fields , a Colorado state representative . `` There 's a lot of hurt . There 's a lot of uncertainty . ''

As the identities of those who died became public Saturday , Town Center at Aurora reopened for business , though its movie house -- Century Aurora 16 -- remained shuttered .

Police Chief Oates said he hoped his officers would be out of the theater by Monday to allow the suspect 's defense team in there Tuesday . Theater owners could get the auditorium back Wednesday , he said .

Investigators have said little about what may have led the suspect to open fire during a premiere Friday of the Batman sequel `` The Dark Knight Rises . '' The sold-out theater was filled with fans , some in costume .

The incident began unfolding late Thursday , when Holmes bought a ticket to the midnight show and entered the theater , a law enforcement source involved in the investigation told CNN .

Families of victims receive tragic confirmation

But Holmes soon went out a rear door leading from the theater to the parking lot , leaving it propped open , the source said . He gathered weapons before re-entering through the same door , said the source , who was not authorized to release the information .

He was back inside the theater a few minutes after the movie had begun and was dressed head-to-toe in black , authorities said .

Witnesses described him as wearing a gas mask that concealed much of his face and head .

Holmes ' hair had been dyed red , and he later told police he was `` the Joker , '' according to a federal law enforcement source with knowledge of the investigation . The source was not authorized to release details to the media .

The federal law enforcement source 's information about the suspect 's appearance fits with a statement made to reporters by New York Police Commissioner Ray Kelly , who said he had been briefed by Colorado authorities .

Police Chief Oates declined to release details about Holmes ' appearance other than to describe what he was wearing : a ballistic helmet and protective gear for his legs , throat and groin , black gloves and a gas mask .

He said he would not release the booking photo `` for investigative reasons . ''

Police said Holmes set off two gas-emitting devices before spraying the theater with bullets from an AR-15 rifle , a 12-gauge shotgun and at least one of two .40 - caliber handguns that police recovered .

`` There was blood everywhere , '' Christina Blache , a shooting victim , told CNN 's Don Lemon from her hospital bed Saturday . Her friend was one of those killed .

`` You 're sitting in a movie theater trying to watch a movie with your friends . Who expects to be shot in a movie theater ? None of us did , '' she said .

Robots reveal unique setup of suspect 's apartment

Holmes had bought the guns legally at stores in the Denver area over the past two months , Oates said . More than 6,000 rounds of ammunition were also purchased online , according to the police chief .

A receipt obtained by CNN shows Holmes bought some of the tactical gear , including a vest and a magazine pouch , online on July 2 .

Want to help ? Here 's how

Holmes surrendered without resistance within seven minutes of the first 911 calls from moviegoers , Oates said . He was arrested in the theater 's rear parking lot .

`` If you think we 're angry , we sure as hell are angry about what has happened to our city , what has happened to these wonderful people who live here , and also what he threatened to do to one of our police officers , '' the police chief said .

Witness : ` Longest minute of my life '

The Joker has long been a fixture in Batman comics and was famously portrayed by Heath Ledger in 2008 's `` The Dark Knight , '' the predecessor to `` The Dark Knight Rises . '' Ledger , who died in 2008 , won a posthumous Academy Award for his portrayal of the villain who encourages anarchists to take over Gotham City .

Holmes , who is being held in Arapahoe County Jail , is scheduled to appear in court on Monday morning . The court file was sealed , according to a court order .

Are you there ? Share your story with CNN iReport and post tributes to the victims .

CNN 's Chelsea J. Carter , Carol Cratty , Ed Lavandera , Susan Candiotti , Joe Sutton , Mike Brooks , Sarah Aarthun and Jim Spellman contributed to this report .

@highlight

NEW : President Obama is scheduled to be in Colorado Sunday to visit victims ' families

@highlight

NEW : `` Who expects to be shot in a movie theater ? '' a survivor asks

@highlight

James E. Holmes received a high volume of deliveries the past four months , says police chief

@highlight

Chief Dan Oates on the suspect 's home : `` Make no mistake . This apartment was designed ... to kill ''